Zembei Mizoguchi, a former top currency diplomat known as “Mr. Dollar” in Japan and former governor of Shimane Prefecture, died Tuesday morning of old age, the prefectural government said Friday. He was 78. Mizoguchi, who joined the Finance Ministry in 1968, served as director general of the International Bureau before becoming vice finance minister for international affairs in 2003. He was known as “Mr. Dollar” for conducting a massive yen-selling, dollar-buying intervention for 15 months from January 2003 in a bid to stem sharp rises in the yen’s value against the U.S. currency. After retiri…